By Stephen Beech on SWNS

As new research shows, sunflowers actually “dance” as they grow to avoid blocking each other’s rays.

The study sheds light on a scientific mystery that has puzzled researchers since the days of Charles Darwin.

Researchers have found that plants growing in dense environments – where each plant casts a shadow on its neighbor – use random movements to find a “collective solution” that helps them find the best direction to grow.

The study, by scientists at Tel Aviv University in Israel, working with colleagues at the University of Colorado at Boulder in the US, sheds light on a puzzle that has puzzled researchers since Darwin, namely the functional role of such inherent movements, called circumnutations.

Lead study author Professor Yasmine Meroz of Tel Aviv University’s Faculty of Plant Sciences and Food Security said: “Previous studies have shown that sunflowers planted densely in a field and shading each other grow in a zigzag pattern – one forward and one backward – so that they do not shade each other.

“In this way, they grow side by side to maximize solar illumination and thus photosynthesis on a collective level.

“In fact, plants know how to distinguish between the shadow of a building and the green shadow of a leaf.

“When they sense the shadow of a building, they usually do not change their growth direction because they ‘know’ it will have no effect.

“But when they sense the shadow of a plant, they grow in a direction away from the shade.”

For the study published in the journal Physical Review X, the researchers investigated how sunflowers “know” that they are growing optimally.

The team analyzed the growth dynamics of sunflowers in the laboratory, where they exhibit a zigzag pattern.

Meroz and her colleagues grew sunflowers in a high-density environment and photographed them as they grew, taking a picture every few minutes.

The photos were then combined into a time-lapse film.

By tracking the movement of each individual sunflower, the team found that the flowers “danced” a lot.

According to researchers, Darwin was the first to realize that all plants exhibit a kind of cyclical movement or “circumnutation” as they grow – both stems and roots exhibit such behavior.

But until now, with the exception of a few cases, such as climbing plants that grow in large circular movements in search of support, it was not clear whether this was a crucial growth trait.

Meroz said: “As part of our research, we conducted a physical analysis that captured the behavior of each individual sunflower within the sunflower group. We found that the sunflowers ‘dance’ to find the best angle so that each flower does not block the sunlight from its neighbor.

“We have statistically quantified this movement and shown through computer simulations that these random movements work together to minimize the amount of shadow.

“It was also very surprising to find that the spread of the sunflower’s ‘steps’ was very large, spanning three orders of magnitude, from a displacement of almost zero to a movement of two centimeters every few minutes in one direction or the other.”

Meroz adds: “The sunflower plant takes advantage of the fact that it can use both small and slow steps and large and fast steps to find the optimal arrangement for the collective.”

“That is, if the spacing of the steps were smaller or larger, the arrangement would result in more mutual shading and less photosynthesis.

“It’s a bit like a crowded dance party where the individual dancers dance around to get more space: if they move too much, they disturb the other dancers, but if they move too little, the crowding problem is not solved because it is very crowded in one corner of the square and empty on the other side.

“Sunflowers show a similar communication dynamic – a combination of response to the shade of neighboring plants and random movements independent of external stimuli.”